Method for forming a semiconductor device by using reverse-offset spacer process

A method for forming a semiconductor device, comprising:

• providing a semiconductor substrate;
• forming a first oxide layer on said semiconductor substrate;
• forming a dummy gate on said semiconductor substrate;
• implanting first ion said semiconductor substrate using said dummy gate as a first mask to form a lightly doped drain region in said semiconductor substrate;
• forming a first spacer on sidewall of said dummy gate;
• implanting second ion said semiconductor substrate using said dummy gate and said first spacer as a second mask to form a source/drain region in said semiconductor substrate;
• forming a first silicide layer on said source/drain region;
• forming a dielectric layer over said semiconductor substrate, and a top surface of said dummy gate is exposed;
• forming a trench by means of removing said dummy gate;
• forming an antipunch-through region under said trench of said semiconductor substrate;
• forming a second spacer in inner sidewall of said trench wherein said second spacer comprises a nitride layer;
• removing said first oxide layer in said trench;
• forming a second oxide layer in said trench;
• forming a gate by means of depositing a conductive layer in said trench;
• and
• forming a second silicide layer on said gate.